Sulfate Respiration in Extreme Environments: A Kinetic Study

Abstract

In situ experiments were conducted in order to quantify sulfate reduction kinetics among thermophilic prokaryotes thriving in hydrothermal springs of Yellowstone National Park (USA). Selected springs were sampled based on their varied physicochemical characteristics in order to identify the effect of extreme environmental determinants over sulfate reduction. Reduction rates range from 1 to 483 nmol cm−3 d−1 in various springs with no correlation observed between sulfate reduction rate and pH or sulfate concentration of spring waters. A weak negative correlation with temperature exists though. Results from slurry incubation experiments show that both the apparent activation energy and the half-saturation constant are site specific. Activation energies of 17, 38, and 119 kJ mol−1 were determined in three different springs whereas the half-saturation constant values of 1.24 ± 0.90 and 3.17 ± 1.02 mM were calculated for two of the sampled springs. Such variations in activity and kinetic parameters may depict a change in the microbial population in different springs, or the response of microbial assemblages to changing physicochemical conditions. In the latter case the sulfate reducers must be highly adaptive to changing environmental conditions.